1. Field of the Invention
The present invention relates to an image forming apparatus and a powder housing unit for use in the image forming apparatus.
2. Description of the Related Art
In image forming apparatuses, e.g., copiers, a residual toner remained on a photosensitive drum or an intermediate transfer belt after transfer of a toner image onto a recording medium or an intermediate member is removed by a cleaning mechanism, and then conveyed to a toner collection box. Thus, the residual toner is gathered together and accumulates in the toner collection box.
A typical toner collection box includes a toner inlet portion that is connected to the cleaning mechanism, a toner conveying unit that conveys the toner coming in the toner conveying unit that conveys the toner coming in the toner collection box to further inside the toner collection box, and a toner-amount monitoring unit that monitors a filling factor indicative of a ratio of the current toner amount to the allowable toner amount in the toner collection box. When the current toner amount reaches the allowable toner amount, i.e., when the toner collection box is full, the toner collection box must be replaced with an empty one.
From the viewpoint of usability, it is preferable to decrease a frequency of replacing the toner collection box. A toner collection box having a larger capacity is suitable in respect of replacement frequency.
More and more small-sized and lower-cost image forming apparatuses have been produced recently. Therefore, it is impractical to use a toner collection box having a large capacity; because a toner collection box having a large capacity increases the overall size of an image forming apparatus.
Generally, a toner collection box is arranged in a dead space in an image forming apparatus, i.e., a space between a feeding unit that is arranged on a bottom of a main body of the image forming apparatus and an image forming unit that is arranged above the feeding unit.
A toner collection box disclosed in Japanese Patent Application Laid-open No. 11-002947 includes a toner conveying unit inside a box-shaped toner cartridge. In this toner collection box, an eccentric cam is attached to a screw shaft that is used for supplying a toner to an outside unit. The eccentric cam causes a plate having projections to horizontally slide back and forth. The projections extend obliquely upward approaching each other and move the toner as the plate slide. A mechanism for sensing a remaining toner-amount is also arranged inside the cartridge.
It is required to ensure a smooth supply of toner to the developing device for avoiding an insufficient toner supply. However, if there is a block of toner in the toner collection box, the block of toner can inhibit the smooth supply. Japanese Patent Application Laid-open No. H05-204281 discloses a mechanism for breaking a block of toner into pieces. In this mechanism, a Mylar film having a pressure-resistance is provided on a portion near an outlet of toner from the screw shaft such that the Mylar film comes in contact with the falling toner. A square rod is arranged such that it comes in contact with the Mylar film. When the square rod rotates, the Mylar film vibrates thereby pushing an upper portion of the accumulated toner downward, i.e., leveling a hill of toner off. As a result it is possible to prevent blocking of toner, and facilitate spreading of the toner.
Japanese Patent Application Laid-open No. H11-002947 discloses a technique to use all toner within the cartridge, i.e., remove all toner from the cartridge by not producing a block of toner. As shown in FIG. 7 of Japanese Patent Application Laid-open No. H11-002947, although toner conveying directions at the pairs of projections extending obliquely upward approaching each other are variable crossing to each other, the toner conveying directions interact with each other to generate a one-way toner conveying direction toward the toner-amount sensing unit. In the mechanism disclosed in Japanese Patent Application Laid-open No. H11-002947, the eccentric cam causes the plate to horizontally slide back and forth so that the toner is conveyed on the plate. The mechanism requires a shaft supporting unit for supporting a rotating shaft attached with the eccentric cam and a plate supporting unit for supporting the plate.
In some cases, the shaft supporting unit is arranged inside the toner collection box for saving the space. The plate supporting unit is, of course, arranged inside the toner collection box. A passage member through which a rotating shaft is arranged is one of simple supporting units that can be replaced with a complicated ball bearing. If a casing of the toner collection box is made by resin molding, such a passage can be formed on a portion of the casing for positioning and supporting of the rotating shaft. The rotating shaft is arranged passing through the passage.
FIGS. 32A and 32B are side views of an exemplary shaft supporting unit 101 that is arranged inside the toner collection box. A cross section orthogonal to a rotation axis is shown. A casing 100 of the toner collection box has two portions, upper and lower, and they are made by resin molding. As shown in FIG. 32A, a passage 100A through which the rotating shaft 101 is passed such that an outer circumference of the rotating shaft 101 engages therewith is formed between the upper portion and the lower portion. As shown in FIG. 32B, a passage 100A′ includes a holding member on the upper portion of the casing 100. A lower circumference of the rotating shaft 101 engages with a part of the passage 100A′ that is on the lower portion, and an upper circumference of the rotating shaft 101 engages with the holding member.
To support the plate, it is possible to form a projection on the plate such that it presses against a bottom of the toner collection box. A supporting unit that extends upward from the bottom of the toner collection box such that the head thereof supports the plate can be used instead of the projection.
The conventional shaft supporting unit supports the rotating shaft in a rotatable manner with a minimum gap between the shaft supporting unit and the rotating shaft. The minimum gap is appropriate for positioning of the rotating shaft. However, the gap is so small that a toner once caught between the shaft supporting unit and the rotating shaft can hardly go out. The toner remained on a bearing makes the gap between the outer circumference of the rotating shaft and a bearing surface uneven, and the uneven gap can cause vibration of the rotating shaft, which can generate noise and abnormal noise.
If a toner is caught between sliding surface of the plate and the plate supporting unit, the toner can causes vibration of the plate, which can generate noise and abnormal noise.
The cause of vibration of the rotating shaft thereby generating noise and abnormal noise is not only the toner remained on the bearing surface. The supporting units can vibrate along with the vibration of the rotating shaft thereby generating noise and abnormal noise.
Most of image forming apparatuses, for example, copying machines, printers, facsimiles, and multifunction products include a cleaning mechanism that removes a residual toner remained on an image carrier after a toner image on the image carrier is transferred onto a paper and a toner conveying unit that conveys the residual toner to the powder housing unit.
For example, Japanese Patent Application Laid-open No. 2006-31006 discloses a powder housing unit that includes inside its casing an agitating mechanism that agitates toners for efficient accommodation. The agitating mechanism includes an agitating plate that is arranged inside the casing, a shaft that extends from the agitating plate to outside of the toner collection unit passing through the casing, a cam member that comes in contact with one end of the shaft, a spring that presses the end of the shaft against the cam member, and a cam driving gear. The cam member rotates to cause the shaft to cyclically press against the spring whereby causes the agitating plate to slide back and forth.
In some powder housing units, a cam member that causes the agitating plate to slide back and forth is arranged inside its casing for saving costs and spaces. However, when the casing is filled with the toner, a part of the toner can be caught between sliding surfaces of a cam member and a bearing of the agitating plate. If a part of the toner is caught between the cam member and the agitating plate, the caught toner generates minute vibration during sliding of the agitating plate. If the cam member, the agitating plate, or any surrounding member vibrates in sympathetic with the vibration, an abnormal noise that annoys surroundings is generated.